Gas discharge tube circuits



Jan. 25, 1938. K. SWART 2,106,287

GAS DISCHARGE TUBE CIRCUITS Filed NOV. 5, 1935 INVENTOR Swazf BY ATTORNEY Patented Jan. 25, 1938 PATENT OFFICE 2,106,287 ens DISCHARGE TUBE omom'rs Leland Kasson Swart, Mountain Lakes, N. 1., a8-

siznor to American Telephone and Telegraph Company,-a corporation of New York Application November 7 Claims.

This invention relates to gas-filled tubes and to circuits'therefor. More particularly, this invention relates to gas-filled tube arrangements adapted to register or record selected types of voltage variations. Still more particularly, this invention is applicable to methods and arrangements for observing and/or recording the heartbeats of man or animal.

The period of the heartbeat of man or animal may be recorded either visually or by the operation of a relay, message register, pen recorder or by other types of recording or alarm arrangements. This statement, however, is based upon the fact that the electromotive forces generated by the heart produce periodic peaks of electromotive force which are of greater amplitude than certain non-periodic electromotive forces generated by muscles and heart, etc.

A simple method for accomplishing this objective consists in the use of an amplifier of high gain to increase the minute voltages produced by the heart to values suflicient to cause operation or ionization of a gas-discharge tube of. for example, the three-element trigger type. An input transformer and condenser may also be employed to tune this circuit to the wave front of the heart voltage peak desired and by virtue of its selective characteristics to exclude other and undesired voltages. The gas-filled trigger tube of the arrangement of this invention is connected to a circuit which causes operation of relays, a message register, pen recorder, etc. Where it is desired that the observations be made only visually, however, only a two-element gas tube need be employed.

It has been determined that the heart produces, among other things, a series of so-called R-waves or voltage peaks at each beat of the heart. The amplitude of these voltage waves is only slightly in excess of other waves produced by the heart which may or may not be periodic. By tuning to the wave front of this R-wave, it is thus possible to obtain increased discrimination between this peak voltage and the undesirable voltages produced, for example, by muscular movement or movements of the heart. By these circuits, as will be shown more clearly hereinafter, the employment of the gas tube arrangement can be made to give a clear-cut distinction between the desired and undesired voltages.

The electromotive forces generated by the heart should be amplified by seventy or eighty decibels. The amplified voltage may be impressed upon the cathodes of a gas-filled or neon tube causing ionization of the gas contained with- 5, 1935, Serial No. 48,380

in the tube. The impedance between the electrodes of the tube is thus reduced, causing current to pass in the secondary circuit which includes the relays and registering or recording apparatus.

This invention will be better understood from the further description hereinafter following when read in connection with the accompanying drawing which shows one embodiment of the in: vention merely for the purpose of illustration.

The terminals I and 2 extend to electrodes which may for instance, be brought in contact with a man or animal. These terminals are shunted by a resistor Z1 which is connected to the grid or input circuit of the tube V1 through a rheostat Z2. The output circuit of the tube V1 includes a coil of inductance L1 through which is supplied plate current from battery or source of potential B. The voltages that are amplified by the tube are applied to the grid or input circuit of another amplifying tube V2 through a condenser C1. The grid of the latter tube is connected to its filament electrode through a drainage coil L2 and the filament of the tube V1. The output circuit of the tube V2 is connected to the source of plate potential B through another 0011 L3. The filaments of both tubes V1 and V2 are connected in series with each other and with the rheostat Z2 and the battery or other source of voltage designated A. The voltages amplified by the second tube V2 are then transmitted through an input transformer T, the primary of which is connected to the output circuit of the tube V: through the adjustable condenser 02.

The secondary winding of the transformer T is in a circuit which includes the cathodes K1 and K2 of a gas-filled discharge tube N, a resistor Z3 and a potentiometer Z4, the outer terminals of which are connected across some or all of the source B. The tap of the potentiometer Z4 may be adjusted so as to bias the cathode K1 with respect to the cathode K2 to any desired potential, which may be below the voltage required to sustain ionization between the cathodes K1 and w or above the sustaining voltage between these electrodes but below the voltage required to initiate gaseous ionization between these electrodes. The anode P of the tube N is connected in a circuit which includes the winding of a relay R1, the winding of an operating relay R2, the source B, the resistor Z3 and the cathode K2 of the tube N. The relay- R1 has its armature and contact connected between the cathode K2 and anode P of tube N through its winding. The armature and contact of the relay R1 are also shunted by a circuit which V 2,106,287 includes the resistor Z5 and the condenser 0;. be employed to record the heartbeats or patients The left-hand terminal of the winding of the during operations, after operations or when it berelay R2 is connected to the armature of the relay R1 by a condenser C4. The armature and contact of the relay R2 are connected in a circuit which includes the source A and a message register or pen recording device or any other recording, registering or indicating device designated MR and this latter device may be located at some remote position.

A foreleg and hind leg 01' an animal, for instance, may be treated with salt and water around which electrodes may be wrapped. The voltage generated by the animal may be applied to the amplifying circuit including the tubes V1 and V2. A predetermined voltage such as that corresponding to the R-wave of the heart may be obtained by adjustment of the condenser 02 and this voltage may be selectively transmitted to the circuits of the gas-filled tube N to the exclusion of all other waves. The biasing voltage of the tube may be adjusted at the tap of the potentiometer Z4 to a value which just records glow between the cathodes K1 and K2 of the tube N and the relay R1 will operate in correspondence to the peak voltages of this R-wave.

In the arrangement shown in the drawing, the armature of the relay R1 will vibrate in accordance with the period of the selected wave. closure of the contact of this relay, the potential between the anode P and the cathode K2 or this tube will be reduced to a practical nullity, the circuit so established including the winding-oi the relay R1 which has a comparatively low resistance or impedance. The vibration of the armature of relay R1 will cause alternate charges and discharges of the condenser Ca through the impedance Z5.

During the vibration of relay R1, current will nevertheless flow through the winding of relay R2. When the armature or the relay R1 is spaced from its contact, the current which traverses the winding of the relay R2 will also traverse the winding of relay R1 as well as the path provided by the anode P and cathode K2 of the tube N. When the armature or the relay R1 closes its contact, current will continue to flow through the winding of the relay R2 over the circuit which includes the armature and contact of the relay R1 and the resistor Z3. In other words, the relay R2 will remain operated as long as the relay R1 continues to vibrate its armature. During the entire period of operation of the relay R2 the message register or other recording device MR will be continuously maintained in operation.

It will be observed that the impedance Z: is common to the circuit of the cathodes K1 and K2 and the circuit of the anode P and cathode K2 of the tube N. When current fiows through this resistor a potential is generated across its terminals which opposes that tapped by potentiometer Z4 from the source B and reduces the effective voltage between the cathodes K1 and K: to a value well below the voltage required to sustain gaseous ionization between these electrodes. This voltage opposition occurs intermittently, i. e., in accordance with the peak voltage selected by the condenser C2 and the input transformer T. It is this poriodic voltage opposition which intermittently deionizes the gas between cathodes K1 and K2 and therefore allows the gas between these cathodes to become ionized only in accordance with the presence of sufilciently amplified voltage derived from the amplifier V1V2.

The arrangement set forth in the drawing may the armature oi. the

At each comes necessary to observe and record any change in the condition of the heartbeat of the patient. Moist electrodes would be strapped to the arm and leg of the patient and fine wires woud be led to the input or the amplifier. The flashing or the neon lamp N or the operation of the relays and the recording device MR will give beats of the patients heart. A plurality of circuits each provided for one of the patients may be so arranged that the various neonlamps may be located at a remote point and there observed by a single attendant.

The apparatus of this invention may be employed in operating rooms during the administration of anaesthetics to enable all present to observe the period of the heart, thus relieving the burdensome observation by other methods which involve the use of the stethoscope, pulse, etc. The apparatus may be also used in the case of diabetic patients where dangerous symptoms leading to convulsions or coma are indicated by the increased rate of the heartbeat. Immediate treatment will prevent the occurrence of these conditions it proper drugs are duly administered, the increase of the period in the heartbeat being thewamlng signal.

If desired, the three electrode device N may be replaced by a two electrode device. Such a device may be bridged across the terminals or the secondary winding 01' transformer T, preferably through a source of biasing voltage, and it would visually indicate the presence of selected, properly amplified voltages obtained from the apparatus connected thereto.

While this invention has been shown and described in a particular arrangement merely for the purpose of illustration, it should be understood that the general principles or this invention may be applied to other and widely varied organizations without departing from the spirit oi the invention and the scope or the appended claims.

What is claimed is:

1. In a heart voltage measuring apparatus, the combination of a tunable amplifier for am.- plifying a selected voltage impressed upon said amplifier to the exclusion of all other voltages, a gas-filled discharge tube having three electrodes, two of which are supplied with the voltage amplified by the amplifier, exhibiting apparatus connected between the third electrode and one of the other electrodes of the tube, and means for periodically deionizing the gas be tween all of the electrodes of the gas-filled tube.

2. In apparatus for measuring heart voltage combination of an amplifier, a gas-filled discharge tube having three electrodes, means for selectively applying only a predetermined voltage to two of the electrodes of the tube, a load circuit connected between the third electrode and one of the other electrodes of the tube, and means for simultaneously deionizing the gas between both pairs of electrodes.

3. Apparatus for observing voltage variations comprising a gas-filled discharge tube having three electrodes, a resistor connected to two of the electrodes, means for selectively applying and magnifying the voltage variations to said two electrodes for producing e. glow discharge between said two electrodes of the tube in response to said selected and magnified voltage variations, and means including a circuit connected between the third electrode and one or the other electrodes and including said resistor for intermittently suppressing the glow discharge between the first two electrodes of said tube during the application of said voltage variations.

4. Apparatus for observing and recording the frequency of a selected alternating voltage to the. exclusion of all other alternating voltages, comprising a tunable circuit for selecting from numerous applied voltages oi diii'erent frequencies 'a voltage of a single frequency substantially to the exclusion of all other frequencies, a gas-filled discharge tube having three electrodes forming two gaps, the selected alternating voltage being applied in magnified form to the electrodes of one of said gaps, exhibiting means connected to the electrodes of the other gap, and means for intermittently deionizing the glow discharge of both gaps.

5. Means for visually indicating the frequenc of an alternating voltage to the exclusion of all other voltages, comprising a gas-filled discharge tube having three electrodes, means selectively responsive to said voltage to ionize the gas between two of the tubes electrodes as well as to ionize the gas between the third electrode and one of the other electrodes, and means responsive to the latter ionization to simultaneously deionize the gas between the two pairs of electrodes already referred to.

6. Apparatus for observing ieeble voltage effier, a tunable circuit connected to the amplifler for selecting predetermined voltage efl'ects, a gas discharge tube of two electrodes connected to said tunable circuit, means responsive to the application of the predetermined voltage effects to said tunable circuit for producing an intermittent glow discharge between the electrodes of said tube for observing the periodicity of the voltage effects, and means responsive to each glow discharge of said tube for producing a voltage for substantially neutralizing the voltage efiect impressed by the tunable circuit between the electrodes of the tube. y

'1. In a heart voltage measuring apparatus, the combination of an adjustable tuned circuit, a gas discharge device having two electrodes coupled to said tuned circuit, a source 0! voltage connected to said circuit, said device producing intermittent observable glow discharge within said device as the frequency of said tuned circuit is made equal to a frequency of said source and means responsive to each glow discharge of said device for producing a voltage to oppose and substantially neutralize the voltage impressed by said tuned circuit on said device. LELAND KASSON SWART. 

